The present embodiments relate to an arrangement with an X-ray detector that is driven by a rotation device.
X-ray systems used in the X-ray field (e.g., C-arm X-ray systems) may be equipped with a device for image rotation. In a C-arm X-ray system, a radiation source and a radiation detector are arranged on a C-shaped arm and may be moved jointly. The C-arm is guided about a patient by a robotic controller. In order to consistently obtain a desired image format when recording a series of images (e.g., a portrait or a landscape), even during a rotation of the C-arm, the ability to rotate the X-ray detector is provided. This makes it possible to adjust the image position using the rotatable X-ray detector during a rotation of the C-arm and to retain the selected image format. FIG. 1 shows a C-arm X-ray system 1 with a rotatable X-ray detector 4. A C-arm 2 bears an X-ray source 3 at one end and the X-ray detector 4, which may be rotated around a vertical axis of rotation 5, at an opposite end.
For precise adjustment of the image position, the respective position of the X-ray detector is to be determined. Rotational speed sensors are used for this purpose, via which an angle of rotation of an initiated rotation is measured in order to undertake control of the drive of the rotation device as feedback. For this purpose, a constant comparison of an actual position measured via the rotational speed sensor with a predetermined setpoint value is undertaken, and the rotational position is adjusted. An optimum measurement of the rotational position is based on measurement of the actual value of the rotational position.
To provide for the safety of an operator of an X-ray apparatus and of a patient to be examined with the X-ray apparatus, two rotational speed sensors may be used to measure the rotational position of the X-ray detector. A collision model for a device movement changes as a function of the respective position of the X-ray detector. To avoid collisions with a table or with the floor, the rotational position are to be reliably determined. Values of the first rotational speed sensor are constantly checked for plausibility using the second rotational speed sensor.
In clinical systems, the X-ray detector is attached to a pulley that is driven by a drive wheel attached to the pulley via a toothed belt. The drive wheel is driven by a motor. The drive wheel is also connected via a further toothed belt to a shaft, to which two rotational speed sensors are attached. The rotational position of the pulley may be determined via the two rotational speed sensors. If the toothed drive belt jumps as a result of mechanical overloading of the axis of rotation of the pulley, this is not detected by either of the two rotational speed sensors, since the two rotational speed sensors are only connected indirectly via the motor shaft to the axis of rotation of the pulley. As a result, an incorrect position of the X-ray detector remains uncorrected, since the axis of rotation of the pulley is not adjusted. A further problem lies in the fact that the two rotational speed sensors are not arranged directly on the shaft of the pulley to be controlled but are attached to the shaft of the pulley by elastic belts. The play in the pulleys also adversely affects the precision of the regulation of the drive based on the measured rotational positions.